Wireless communication systems allow wireless devices to communicate without the necessity of wired connections. Because wireless systems have become highly integrated into daily life, there is a growing demand for wireless communication systems that support multimedia services such as speech, audio, video, file and web downloading, and the like. To support these multimedia services for wireless devices, various wireless communication protocols have been developed to accommodate the growing demands of multimedia services over wireless communication networks.
One such protocol is Wideband Code Division Multiple Access (W-CDMA), which is promulgated by the 3rd Generation Partnership Project (3GPP™), a collaboration of numerous standards development organizations. W-CDMA is a wideband spread-spectrum mobile air interface that uses a direct sequence Code Division Multiple Access (CDMA).
In some embodiments, W-CDMA may support Universal Mobile Telecommunications Systems (UMTS). A UMTS communication system may provide telephony and bearer services in connectionless and connection-oriented communication networks, offering both Point-to-Point (P2P) and Point-to-Multipoint (P2MP) communication. In some UMTS communication systems, the air interface access method may be based on Universal Terrestrial Radio Access Networks (UTRAN), also called UMTS Terrestrial Radio Access Network (also referred to as UTRAN), or Evolved UTRAN (E-TRAN), also referred to as Long Term Evolution (LTE).
Another such protocol is Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard based protocol that use orthogonal frequency division multiple access (OFDMA). An IEEE 802.16m communication system, often called a worldwide interoperability for microwave access (WiMAX) system, provides wireless broadband data, voice, and multimedia services to user.
Wireless communication systems typically operate either in Frequency Division Duplex (FDD) or Time Division Duplex (TDD) mode. In a FDD system, uplink transmission and downlink transmission operate on different channels, or different frequencies, and wireless devices operating in such a FDD system can transmit and receive simultaneously. In a TDD wireless communication system, however, uplink and downlink transmissions may take place over the same communication channel by physically taking turns in the channel. In some systems, such as an upcoming 4G wireless system, TDD is advantageous because asymmetrical data exchange can be supported more efficiently. For example, a spectrum utilization rate can be increased in TDD systems when the system is transmitting asymmetrically.
FIG. 1 is a signaling diagram illustrating a prior art TDD frame structure for an exemplary wireless communication system. A frame 100 may consist of a plurality of time periods available for a downlink or uplink transmission referred to as Transmission Time Intervals (TTIs) 102. As shown in FIG. 1, frame 100 may include an uplink subframe 104 and a downlink subframe 106. Using uplink subframe 104, a downlink node 108 may transmit uplink transmissions 110 for receipt, for example, at an uplink node 112. During downlink subframe 106, uplink node 112 may transmit downlink transmissions 114 for receipt, for example, at downlink node 108. Uplink subframe 104 and downlink subframe 106 may each include any number of TTIs 102, so the size of frame 100 may vary. In some variations, the structure of frame 100 may be dynamically adapted according to the ratio of uplink data to be transmitted to downlink data to be transmitted.
A radio interface protocol stack for W-CDMA may include support for error detection. Automatic Repeat Request (ARQ) and Hybrid Automatic Repeat Request (HARQ) are two error detection methods used to control errors when transmitting data across a wireless network. In ARQ, a receiver detects frame errors and requests retransmissions. HARQ is a variation of the ARQ error control method in which forward error correction bits are also added to correct frame errors.
In some variations, HARQ can be configured to operate using a Stop-And-Wait (SAW) mode or a Selective Repeat (SR) mode. In SAW mode, a HARQ transmitter must wait for a HARQ feedback packet such as an acknowledgement (ACK) or negative acknowledgement (NACK) from the HARQ receiver before transmitting or retransmitting the next data packet. In some variations, an associated control signal including a 1-bit sequence number may be used to distinguish between new transmissions and retransmissions. During the waiting period for the HARQ feedback packet, the transmission channel may go unused.
A transmitting device, or transmitting station, may include a HARQ transmitting (HARQ Tx) mechanism. Similarly, a receiving device, or receiving station, may include a HARQ receiving (HARQ Rx) mechanism. The HARQ Tx and HARQ Rx mechanisms may be any combination of software and/or hardware components configured to cause the transmitting and/or receiving devices to perform the functions of sending and/or receiving HARQ transmissions. The HARQ Tx and HARQ Rx mechanisms may reside in MAC sub-layers of the transmission and receiver devices, respectively.
FIG. 2 is a signaling diagram illustrating a prior art transmission using a single HARQ process. In one variation, a HARQ process is an instance of a stop and wait (SAW) protocol, and may be used to control the transmission/retransmission of data. As shown in FIG. 2, a HARQ Tx 202 transmits a data packet 204 to a HARQ Rx 206. HARQ Tx 202 may encode data packet 204 prior to transmission, and HARQ Rx 206 may decode data packet 204. If an error is detected, the received packet data 204 may be discarded and HARQ Rx 206 may request a retransmission by transmitting NACK 208 to HARQ Tx 202. Upon receiving NACK 208, HARQ Tx 202 retransmits a data packet 204′ to HARQ Rx 206. After data retransmission data packet 204′ is properly received at HARQ Rx 206, HARQ Rx 206 may transmit ACK 210 to HARQ Tx 202, which can then transmit a new data packet 212 to HARQ Rx 206.
A multi-channel version of SAW mode HARQ, using a number N of parallel HARQ processes, may improve transmission efficiencies, for example by reducing control signal overhead. While awaiting the HARQ feedback packet (ACK/NACK) for previously transmitted packet data, other transmissions can be sent. In one variation, a HARQ process identifier, or HARQ process ID, is included in the transmission so HARQ Rx 206 can identify the HARQ process corresponding to a received packet data.
FIG. 3 is a signaling diagram illustrating a prior art transmission having multiple HARQ processes. As shown in FIG. 3, HARQ Tx 202 transmits a data packet 302 from a second HARQ process after data packet 204 is transmitted from a first HARQ process. HARQ Rx 206 transmits an ACK 304 to HARQ Tx 202 upon successful receipt of data packet 302. HARQ Tx 202 may then transmit a new data packet 306 to HARQ Rx 206.
In accordance with the IEEE 802.16 family of standards, HARQ can be configured as synchronous or asynchronous with adaptive or non-adaptive modulation and may include coding schemes for different types of HARQ processing, such as chase combining or incremental redundancy operation. When synchronous HARQ is implemented, HARQ transmissions/retransmissions may be transmitted only at predetermined times. In a FDD system, due to the continuous uplink and downlink transmissions over separate channels, synchronous HARQ can be implemented by using the same Round Trip Time (RTT). The HARQ process corresponding to a particular data packet or HARQ feedback packet can be determined using a feedback time slot. In a TDD system, multiple data packets or HARQ feedback packets may be received at a single time slot so a feedback time slot alone may not be sufficient for determining a HARQ process ID.
Further, when synchronous HARQ is implemented in a more advance IEEE 802.16m standard based system, it may be more difficult to determine time parameters associated with a HARQ retransmission and/or HARQ feedback packet.